Alex has been captured and Tom, Kyra, and Jack must scramble to find him. As Scorpia shows the power of their new weapon, Invisible Sword, Alex is confronted by Julia Rothman with some uncomfortable truths about his father.

Cut off from his friends and forced to work with one of his greatest foes, Alex endures a punishing induction to Scorpia, and must face off against a gang of ruthless trainee assassins.

Alex is sent on a mission for Scorpia to prove his loyalty, with Tom and Kyra following close behind hoping to rescue him. Meanwhile, the Department attempts to unlock the secret of 'Invisible Sword'.